Image augmented inertial navigation system (iains) and method

ABSTRACT

An image-augmented inertial navigation system includes an inertial navigation system configured to estimate a navigation state vector and an imager configured to output pixel signals associated with terrain features passing through a field view of the imager. The system further includes a processing unit configured to determine a distance from the imager to each of the pixel signals for a given image frame and to determine a distance between the imager and a centroid of one or more of the terrain features passing through the field of view of the imager for the given image frame. The processing unit is also configured to track each terrain feature as the terrain features pass through the field of view of the imager. The processing unit is further configured to update the navigation state vector of the inertial navigation system based on calculated NED coordinates position information of the tracked terrain features.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Application No. 60/576,037, filed on Jun. 2, 2004,the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to systems and methods for navigating avehicle. In particular, the present disclosure relates to animage-augmented inertial navigation system and method for a vehicle.

BACKGROUND OF THE INVENTION

The general methodology of a loosely-coupled inertial navigation system(INS) implements two steps for determining estimates of the navigationstate vector of a body: (1) propagation of the navigation state vectorvia numerical (or other) integration of sensed accelerations and ratesof the body, and (2) updates (or corrections) to the navigation statevector using external aiding sources. The external aiding source may beone or more of a wide variety of sources, the most common beingsatellite based navigation systems such as, for example, the USA'sglobal positioning system (GPS). Such INS solutions are used for vehiclenavigation, whether they are ground, air, space, or sea going vehicles.Sometimes, however, external aiding sources, such as GPS may becomeunavailable due to various reasons. For example, GPS may be jammed ormay become unavailable due to location.

One possible way to overcome the unavailability of external aidingsources such as GPS includes traditional navigation by image processing.Traditional navigation by image processing registers the location of anewly detected image with respect to a known, stored image. Upon suchsuccessful geo-registration, the North, East, and Down (NED) coordinatesof the image location may be used as an external aiding source to updatethe INS derived navigation state vector. Such image basedgeo-registration typically requires, however, a very powerful computerprocessing unit (CPU) since real-time geo-registration is very CPUintensive. Use of a very powerful CPU may be prohibitively expensive ormay require space unavailable for certain applications.

As a result of the above-mentioned drawbacks, it may be desirable toprovide a navigation system that enables a vehicle carrying such asystem to obtain a continuous navigation solution, even in conditionswhere NED external aiding sources such as GPS become unavailable.Furthermore, it may be desirable to provide a navigation system thatdoes not require a powerful CPU.

There may exist a desire to overcome one or more of the above-mentioneddrawbacks. The exemplary disclosed systems and methods may seek tosatisfy one or more of the above-mentioned drawbacks. Although thepresently disclosed systems and methods may obviate one or more of theabove-mentioned drawbacks, it should be understood that some aspects ofthe disclosed systems and methods might not necessarily obviate them.

SUMMARY OF THE INVENTION

In the following description, certain aspects and embodiments willbecome evident. It should be understood that the invention, in itsbroadest sense, could be practiced without having one or more featuresof these aspects and embodiments. It should be understood that theseaspects and embodiments are merely exemplary.

In one aspect, as embodied and broadly described herein, the inventionincludes an image-augmented inertial navigation system including aninertial navigation system configured to estimate a navigation statevector and an imager configured to output pixel signals associated withterrain features passing through a field view of the imager. The systemfurther includes a processing unit operatively connected to the inertialnavigation system and the imager. The processing unit is configured todetermine a distance from the imager to a centroid of one or more of theterrain features passing through the field of view of the imager for agiven image frame based on the pixel signals. The processing unit isalso configured to track each terrain feature from a first image frameto a second image frame as the terrain features pass through the fieldof view of the imager and calculate NED coordinates position informationof each tracked terrain feature. The processing unit is furtherconfigured to update the navigation state vector of the inertialnavigation system based on the calculated NED coordinates positioninformation.

According to another aspect, a vehicle includes an image-augmentedinertial navigation system. The system includes an inertial navigationsystem configured to estimate a navigation state vector and an imagerconfigured to output pixel signals associated with terrain featurespassing through a field view of the imager. The system further includesa processing unit operatively connected to the inertial navigationsystem and the imager. The processing unit is configured to determine adistance from the imager to a centroid of one or more of the terrainfeatures passing through the field of view of the imager for a givenimage frame based on the pixel signals. The processing unit is alsoconfigured to track each terrain feature from a first image frame to asecond image frame as the terrain features pass through the field ofview of the imager and calculate NED coordinates position information ofeach tracked terrain features. The processing unit is further configuredto update the navigation state vector of the inertial navigation systembased on the calculated NED coordinates position information.

According to yet another aspect, a method of updating a navigation statevector of an inertial navigation system associated with a vehicleincludes determining a distance from an imager associated with thevehicle to a centroid of one or more terrain features passing through afield view of the imager for a given image frame. The method furtherincludes tracking each terrain feature from a first image frame to asecond image frame as the terrain features pass through the field ofview of the imager. The method also includes calculating NED coordinatesposition information for each of the tracked terrain features andupdating the navigation state vector of the inertial navigation systembased on the calculated NED coordinates position information.

Aside from the structural and procedural arrangements set forth above,the invention could include a number of other arrangements, such asthose explained hereinafter. It is to be understood, that both theforegoing description and the following description are exemplary.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is incorporated in and constitutes a part ofthis specification. The drawing illustrates an exemplary embodiment ofthe invention and, together with the description, serves to explain someprinciples of the invention. In the drawing,

FIG. 1 is a schematic view of a vehicle oriented in a NED coordinatesystem, including an exemplary image-augmented inertial navigationsystem.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to some possible exemplaryembodiments of the invention, an example of which is illustrated in theaccompanying drawing. Wherever possible, the same reference numbers areused in the drawing and the description to refer to the same or likeparts.

An exemplary image-augmented inertial navigation system (IAINS) includesan INS and an imaging payload that enables a vehicle carrying such anIAINS to obtain a continuous navigation solution, even in conditionswhere NED external aiding sources may become unavailable.

As schematically-depicted in FIG. 1, a host vehicle 10, such as forexample, an airplane, carries an imager 12. The imager 12 may be, forexample, a camera, lidar, radar or other similar device known to aperson having ordinary skill in the art. The imager 12 may include a CPUor the CPU may be located separate from the imager 12. The imager 12 isaimed in the direction of a scene (e.g., a feature of the terrain overwhich the vehicle 10 is flying) to be imaged. There is no constraint onthe orientation of the imager 12 with respect to the vehicle 10 and INSaxes (x, y, z). Such an orientation may be either fixed or it may changein real-time, so long as the imager 12's orientation and offset is knownwith respect to the vehicle 10 and the INS axes at all times.

As the vehicle 10 moves over the terrain, the imager 12 observes a sceneon the ground and projected images of the scene will move across theimage plane of the imager 12. For simplicity, FIG. 1 depicts the imager12's view direction as directly coincident with the vehicle 10 and INSz-axis, where the vehicle 10 and INS axes have aligned axes systems,although this is not required.

According to an exemplary image-augmented inertial navigation system,the concept combines two capabilities: (1) the capabilities of an INSsystem, and (2) the capabilities of an external aiding source. Thecombination provides data including (a) a pixel array of imageinformation in image coordinates, (b) an associated range valuerepresenting the relative distance from the imager 12 (e.g., radar,lidar, video, or any other imaging system) to the ground location of afeature represented by the pixel, and (c) automated tracking of thefeature as it moves through the image. The image-augmented navigationsystem according to some embodiments requires minimal image processingcapability, thereby rendering a powerful CPU unnecessary. In fact, itmay be sufficient, according to some embodiments, to identify highcontrast features in the image plane and track the identified featuresfrom frame to frame, as the identified features move through the imager12's field of view.

For example, the image-augmented inertial navigation system relativenavigation external aiding source is used for navigation state vectorupdates in the following ways:

A. While an NED coordinates external aiding source is available:

-   -   1. the NED coordinates external aiding source could be a GPS, or    -   2. geo-registration by automatic recognition of landmarks in the        image, ground based radar, or any other external aiding source        that provides information in the form of NED coordinates        location of the INS. This direct NED coordinates update to the        INS navigation state vector occurs whenever such an external        aiding source update becomes available.

B. When a new feature in the external aiding source begins to be trackedin the image: immediately upon first receipt of a newly identifiedfeature, the NED coordinates location of this new i^(th) trackedfeature, Xo_(i)(N,E,D), is tagged and frozen until such time as itleaves the imager 12's field of view. This may be achieved by projectingrange between the actual feature and the imager 12, from the currentknown location of the INS via the image orientation and offset withrespect to the INS.

C. When a new image becomes available and provides new information aboutall tracked features:

-   -   1. All of the tracked features must already be at least one        image frame old, and each feature has an initial NED location        defined by    -   2. As the new image becomes available, determine the new        image-based NED coordinates position estimate of the INS        relative position referenced to each of the currently tracked        features based on the following equation:

X(t)_(i) =Xo _(i)(N,E,D)+CR(t),

where C R(t) represents the projected range via imager orientation andoffset with respect to the INS

-   -   3. Use each of the NED position estimates of the INS calculated        relative to each feature, X(t)_(i), as an NED position update to        the INS.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure andmethodology of the present disclosure. Thus, it should be understoodthat the disclosure is not limited to the examples discussed in thespecification. Rather, the present disclosure is intended to covermodifications and variations.

1. An image-augmented inertial navigation system comprising: an inertialnavigation system configured to estimate a navigation state vector; animager configured to output pixel signals associated with terrainfeatures passing through a field view of the imager over a plurality ofimage frames; and a processing unit operatively connected to theinertial navigation system and the imager, the processing unit beingconfigured to sense a distance from the imager to a centroid of one ormore of the terrain features passing through the field of view of theimager for a given image frame based on the pixel signals, track eachterrain feature from a first image frame containing the terrain featureto any subsequent image frame while the terrain features remain withinthe field of view of the imager, calculate NED coordinates positioninformation of the inertial navigation system relative to first taggedcoordinates of each tracked terrain feature, and update the navigationstate vector of the inertial navigation system based on the calculatedinertial navigation system position information.
 2. The system of claim1, wherein the processing unit is configured to track new terrainfeatures as they pass within the field of view of the imager bydetermining the distance between the imager and the new terrain featuresand by predicting a distance between the new terrain features and theimager based on a current known location of the inertial navigationsystem.
 3. The system of claim 1, wherein the processing unit isconfigured to determine and tag NED coordinates position information fornew terrain features a first time the new terrain features enter intothe field of view of the imager, based on the current inertialnavigation system position, range to the new terrain feature,orientation and offset of the imager with respect to the inertialnavigation system.
 4. A vehicle comprising the system of claim
 1. 5. Amethod of updating a navigation state vector of an inertial navigationsystem associated with a vehicle, the method comprising: sensing adistance from an imager associated with the vehicle to a centroid of oneor more terrain features passing through a field of view of the imagerfor a given image frame; tracking each terrain feature from a firstimage frame to a subsequent image frame as the terrain features passthrough the field of view of the imager; calculating NED coordinatesposition information for each of the tracked terrain features; andupdating the navigation state vector of the inertial navigation systembased on the calculated NED coordinates position information.
 6. Themethod of claim 5, further comprising tracking new terrain features asthey pass within the field of view of the imager by determining thedistance between the imager and the new terrain features and bypredicting a distance between the new terrain features and the imagerbased on a current known location of the inertial navigation system. 7.The method of claim 5, further comprising determining and tagging NEDcoordinates position information for new terrain features a first timethe new terrain features enter into the field of view of the imagerbased on a current inertial navigation system position, range to theterrain new feature, orientation and offset of the imager with respectto the inertial navigation system.